Recently, in line with miniaturization, lightweight, thin profile, and portable trends in electronic devices according to the development of information and telecommunications industry, the need for high capacity and long life batteries used as power sources of such electronic devices has increased. Since a lithium secondary battery, specifically, a lithium ion battery (LIB) has high energy density and its design is easy, the lithium ion battery has been adopted as a powder source of many portable devices.
Recently, research into positive electrode active materials and negative electrode active materials having high capacity and improved cycle life characteristics as materials for the lithium ion battery has been expanded as the lithium ion battery is adopted as a power source for an electric vehicle or power storage in addition to applications such as portable IT devices.
As the negative electrode active materials, non-carbon-based negative electrode active materials having significantly higher capacity per unit weight than that of typically used carbon have been actively researched.
Among these non-carbon-based negative electrode active materials, a silicon-based composite active material, for example, a Si/C active material is an active material in the form in which a silicon layer is formed on the surface of a carbon-based negative electrode active material, wherein, since it is known to have excellent discharge efficiency (80%) as well as higher capacity than theoretical capacity (about 372 mAh/g) of the carbon-based negative electrode active material, it is in the spotlight as a high-capacity secondary battery material.
However, with respect to a silicon-based active material, since achievable capacity is limited and swelling is large, deformation, such as cracks, occurs in the active material during charge and discharge cycles, and thus, it becomes a cause of degradation of life characteristics due to the cycles of the battery.
Therefore, in order to address such limitations, there is an urgent need to develop a silicon-based negative electrode active material, which may improve discharge capacity, initial efficiency, and output characteristics when used in a lithium secondary battery, and a secondary battery including the same.